High molecular weight polymers as viscosity modifiers

ABSTRACT

A lubricating composition comprises a base oil and between  10  ppm and  1000  ppm of a viscosity modifier, the viscosity modifier comprising a polymer having a number average molecular weight greater than  500,000.  The polymer is preferably selected from the group consisting of ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-propylene-acrylate copolymers, ethylene-propylene-methacrylate copolymers, ethylene-propylene-aromatic copolymers, ethylene-propylene-diene-acrylate copolymers, ethylene-propylene-diene-methacrylate copolymers, and combinations thereof.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/562,552, filed on Nov. 22, 2011, the entirety of which is herein incorporated by reference.

FIELD OF THE INVENTION

The invention relates to the use of ultra-high molecular weight polymers as viscosity modifiers and more particularly to the use of low concentrations of ultra-high molecular weight copolymers as viscosity modifiers in lubricating oils and similar compositions. The resulting lubricating oils are particularly advantageous in direct injection engines.

BACKGROUND OF THE INVENTION

In internal combustion engines, gasoline direct injection (GDI) is a type of fuel injection system that may be used in two-stroke and four-stroke engines. In contrast to conventional carburetor or port injection systems in which fuel is supplied upstream of the cylinder inlets, in a GDI system, the fuel is pressurized and injected directly into the combustion chamber of each cylinder. In modern engines the injection can be finely controlled so as to minimize heat loss and combustion inefficiency. Thus, the major advantages of a GDI engine are increased fuel efficiency and higher power output.

Conventional wide span lubricants contain polymers that serve as Viscosity Index Improvers (VIIs), which are a necessary component of multi-grade oils. In port injected engines, fuel washes the back on the intake valve and helps prevent the formation of deposits there. Even so, in conventional engines, the polymer additives contribute to engine deposits, which are in turn controlled with other additives.

In GDI engines, this washing does not occur and cylinder intake valves can accumulate high levels of deposits, which tend to impair engine performance. Viscosity modifiers present in the engine lubricating oil contribute to the formation of these deposits by degrading on hot surfaces, particularly on the back of intake valves, creating deposits that can restrict air flow into the combustion chamber, thereby reducing engine efficiency. Thus, it would be advantageous to greatly reduce the VII concentration in modern engine oils so as to reduce or prevent intake valve deposits.

For narrow span oils like SAE 5W-20, this can be accomplished by using synthetic base oils, also referred to as gas to liquids (GTL), poly-alpha olefins (PAOs) base oils or other base stocks with sufficiently high viscosity index. When shifting to a wider span multi grade oil like SAE 0W-20 or wider oils, however, VIIs are still required. Thus, it is desirable to provide an engine oil that has the desired viscometric properties without including viscosity modifiers at a level that causes unacceptable levels of deposit formation.

SUMMARY OF THE INVENTION

In accordance with preferred embodiments of the invention there is provided an engine oil that has desirable viscometric properties and greatly reduced viscosity modifier (VM) treat levels, thus reducing the tendency of forming intake valve deposits which can reduce engine performance, decreasing fuel economy and increasing carbon dioxide emissions.

According to certain embodiments, a composition for lubricating an engine according to the present invention comprises a base oil and between 10 ppm and 1000 ppm of a viscosity modifier wherein the viscosity modifier is a polymer having a number average molecular weight greater than 500,000. The polymer preferably comprises ethylene and propylene and more preferably comprises at least 50 percent by weight ethylene and propylene.

The polymer is preferably selected from the group consisting of, but not limited to, ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-propylene-acrylate copolymers, ethylene-propylene-methacrylate copolymers, ethylene-propylene-aromatic copolymers, ethylene-propylene-diene-acrylate copolymers, ethylene-propylene-diene-methacrylate copolymers, and combinations thereof.

Preferred polymers for use in the present compositions have molecular weights greater than 1,000,000, more preferably greater than about 2,000,000, and in some instances greater than about 5,000,000. The concentration of the polymer is preferably between 10 ppm and 500 ppm when used as the sole VM and/or it may be combined with other VMs known to those skilled in the art.

A composition according to the present invention preferably has a viscosity index (VI) greater than 150, more preferably greater than 175, and still more preferably greater than 200. While inspecting the properties of motor oils formulated with the ultra-high molecular weight polymers we found that the viscosity index (VI) of the oils was significantly and unexpectedly high. VI values greater than 200 are normally the result of using high treat rates of polymethacrylate VI improvers; it was surprising to find VIs over 200 that were achieved using low treat rates of the present hydrocarbon VI improvers.

When used as lubricants, the present compositions may also include at least one additional component selected from the group consisting of but not limited to additional viscosity modifiers, anti-wear additives, dispersants, detergents, pour point depressants, friction modifiers, corrosion inhibitors, anti-oxidants, and other additives such as are known in the art.

In other embodiments, the present invention is used to formulate fuels, greases, transmission oils, hydraulic oils, gearbox oils, marine oils, and the like, and may in such formulations be combined with other suitable additives.

DETAILED DESCRIPTION

According to preferred embodiments of the invention, an effective engine lubricating oil can be provided by blending a base oil with at least one ultra-high molecular weight polymer. The polymer can be included in the base oil at very low concentrations, or treat rates, with the result that deposits accumulate in an engine at a much lower rate than would otherwise occur.

Base Oil

Base oils suitable for use in the present invention include base oils as described in API publication 1509, which includes Group I, Group II, Group III, Group IV, and Group V oils, and mixtures thereof, optionally in combination with other base oils. API 1509 describes the base oil groups and those skilled in the art can employ the current invention by using those base oils with SAE J300, SAE J306, and other industry documents to create useful lubricating compositions. These engine oils will have functional properties known to those skill in the art such that they comply with SAE J300, API 1509, ILSAC GF-5, SAE D4485 and others.

Polymer

The ultra-high molecular weight polymer or polymer blend may be present at concentrations ranging from 10 ppm to 1000 ppm, preferably from 10 ppm to 500 ppm, and more preferably from 50 ppm to 250 ppm. Concentrations in this range can be achieved by pre-blending the polymer into a base oil concentrate, so that it can later be added to the formulation as a liquid, by blending directly into the formulation, or by blending it into a solvent for delivery into the final formulation.

Ultra-high molecular weight polymers suitable for use in the present compositions are those formed from blends comprising ethylene and propylene monomers and having molecular weights of at least 500,000. In preferred embodiments, the molecular weight of at least one polymer is greater than 1,000,000, more preferably greater than 2,000,000, more preferably greater than 5,000,000, and more preferably greater than 10,000,000.

The polymer is preferably an olefin copolymer selected from the group consisting of, but not limited to, ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-propylene-acrylate copolymers, ethylene-propylene-methacrylate copolymers, ethylene-propylene-aromatic copolymers, ethylene-propylene-diene-acrylate copolymers, ethylene-propylene-diene-methacrylate copolymers, and combinations thereof. One compound that is particularly preferred for use in the invention is available from ConocoPhillips of Houston, Tex. under the name LP™ 100 Flow Improver.

Also suitable for use are synthetic rubber compounds, nitro- and oxy-functionalized olefin copolymers, antioxidant-grafted copolymers, dispersant-grafted copolymers, and combinations thereof.

For additional specific polymer compositions that can be used in the present inventions and for methods of making them, reference is made to U.S. Pat. Nos. 4,693,321, 5,539,044, 5,376,697, 6,172,151, 6,399,676, 6,576,732, 6,596,832, 6,765,053, 6,939,902, 7,285,582, 7,361,628, 7,763,671, 7,888,407, and European Patent EP0196350, each of which is incorporated herein in its entirety.

The inventive polymer typically contains ethylene and propylene in ratios normally seen in other E/P polymers consisting from about 10 to 70% ethylene and from about 20 to 90% propylene, with additional monomer optionally included. Increasing the ethylene content increases thickening power but decreases solubility in certain base fluids. Thus the skilled practitioner will choose polymer compositions suited to the specific use intended.

The use of additional monomers is also anticipated to allow the inventive polymer to have the properties of dispersants, antioxidants, pour point depressants and other additive chemistry known to those skilled in the art.

Additives

In addition to the ultra-high molecular weight polymers, various additives are known for use in lubricating compositions may be included in the present lubricating composition. These include but are not limited to detergents, dispersants, anti-wear agents, anti-oxidants, pour point depressants, corrosion inhibitors, friction modifiers, anti-foaming agents and additional viscosity modifiers, all of which are known in the art, which may be added separately or in combination so as to enhance to lubricant formulations performance.

In some preferred embodiments a lubricating composition includes both an ultra-high molecular weight polymer and a second viscosity modifier selected from the group consisting of those currently used by those skilled in the art, which include but are not limited to olefin copolymers (OCPs), E/P, EPDM, Styrene—isoprene, Styrene-butadiene, polyacrylates and polymethacrylates and others. If present, the second viscosity modifier may be present in an amount ranging from 0.1 wt % to 10 wt %. By way of example only, such additives include those disclosed U.S. Pat. Nos. 3,522,180; 4,026,809; 4,146,489; 4,340,689; and 4,780,689, which are each incorporated herein by reference.

U.S. Pat. No. 3,522,180 discloses a method for the preparation of an ethylene-propylene copolymer substrate effective as a viscosity index improver for lubricating oils. U.S. Pat. No. 4,026,809 discloses graft copolymers of a methacrylate ester and an ethylene-propylene-alkylidene norbornene terpolymer as a viscosity index improver for lubricating oils. U.S. Pat. No. 4,146,489 discloses a graft copolymer where the polymer backbone is an oil-soluble ethylene-propylene copolymer or an ethylene-propylene-diene modified terpolymer with a graft monomer of 2- or 4-vinylpyridine or N-vinylpyrrolidone to provide a dispersant VI improver for lubricating oils. U.S. Pat. No. 4,340,689 discloses a process for grafting a functional organic group onto an ethylene-propylene copolymer or an ethylene-propylene-diene terpolymer. U.S. Pat. No. 4,780,228 discloses the grafting of a hydrocarbon polymer in the absence of a solvent in the presence of a free radical initiator and a chain-terminating agent followed by a reaction with an amine, polyol or an aminoalcohol.

EXAMPLES

It has been discovered that inclusion of an ultra-high molecular weight polymer in an engine oil can significantly increase the viscosity index, even at extremely low treat rates. For example, VI increases of 30 points were observed in more than one instance, which was most unexpected. Table 1 below gives some test results showing the surprising improvement in VI.

TABLE 1 Lubricating Oil Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 4 KV40 (cSt) 45.14 35.2 43.72 32.38 Kv100 (cSt) 9.72 7.348 8.513 6.371 VI 208 181 176 152 CCS-35 (cP) 5580 5110 5590 5140

In Table 1, all Examples are based on a commercially available, additive-containing SAE 0W-20 lubricating oil. Examples 1 and 2 consisted of the commercially available SAE 0W-20 oil plus 100 weight ppm of LP™ 100 Flow Improver from ConocoPhillips of Houston, Tex. In Example 1, a commercially available lubricant was used as-sold. In Example 2, a viscosity modifier that was present in the commercial lubricant, namely a hydrogenated isoprene star polymer with a shear stability of between 10 and 20 percent viscosity loss in the finished lubricant using the Kurt Orbahn shear stability test, comprising 4.5 wt. percent of the commercial lubricant, was removed from the formulation. It was found that a stirring bar or paddle mixer is preferred over a high-shear blender for mixing the compositions, as the latter tends to reduce the viscosity of the final composition. In contrast, Comparative Examples 3 and 4 contained no LP™ 100 Flow Improver. Otherwise, Comparative Examples 3 and 4 consisted of the same lubricants as Examples 1 and 2, namely commercially available SAE 0W-20 oil with and without, respectively, 4.5 wt. percent of the viscosity modifier described above.

The VI of 208 achieved by Example 1 is unheard of in hydrocarbon systems that do not include PMA thickeners and may have strong fuel economy implications. In addition, it is expected that the use of a lubricant containing such a low concentration of polymer would lower the probability of the polymer coming into contact with the back of the intake valves, thereby reducing the rate at which deposits will form. It is further noted that in Example 1, addition of the flow improver increases the KV 100 such that the oil shifts into the 0W-30 range.

It has further been discovered that inclusion of an ultra-high molecular weight polymer in a gear oil can significantly increase the viscosity index. Table 2 below gives some transmission fluid test results.

TABLE 2 Transmission Fluid Comp. Ex. 5 Ex. 6 KV40 (cSt) 31.42 27.60 Kv100 (cSt) 6.954 6.05 VI 192 176

In Table 2, the Examples are based on a commercially available SAE J306 transmission fluid. Example 5 consisted of the commercially available transmission fluid plus 100 weight ppm of LP™ 100 Flow Improver from ConocoPhillips of Houston, Tex. Comparative Example 6 consisted of the commercially available transmission fluid with no added flow improver. As can be seen, the viscosity index of the transmission fluid went from 176 to 192.

It is expected that compositions according to the present claims will help increase efficiency and those reduce fuel consumption when used to lubricate internal combustion engines and in particular gasoline direct injection engines. It is further expected that the compositions according to the present invention will provide other advantages when used in other applications, including as transmission oils, hydraulic oils, gearbox oils, and/or marine oils. 

What is claimed is:
 1. A lubricant composition, comprising: a base oil; and between 10 ppm and 1000 ppm of a viscosity modifier, the viscosity modifier comprising a polymer having a number average molecular weight greater than 500,000.
 2. The composition according to claim 1 wherein the polymer comprises ethylene and propylene.
 3. The composition according to claim 1 wherein at least 50 weight percent of the polymer comprises ethylene and propylene.
 4. The composition according to claim 1 wherein the base oil is selected from API group I, group II, group III, group IV, group V and combinations thereof.
 5. The composition according to claim 1 wherein the polymer is selected from the group consisting of ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-propylene-acrylate copolymers, ethylene-propylene-methacrylate copolymers, ethylene-propylene-aromatic copolymers, ethylene-propylene-diene-acrylate copolymers, ethylene-propylene-diene-methacrylate copolymers, and combinations thereof.
 6. The composition according to claim 1 wherein the polymer has a molecular weight greater than 500,000.
 7. The composition according to claim 1 wherein the polymer has a molecular weight greater than 1,000,000.
 8. The composition according to claim 1 wherein the polymer has a molecular weight greater than 2,000,000.
 9. The composition according to claim 1 wherein the polymer has a molecular weight greater than 5,000,000.
 10. The composition according to claim 1 wherein the concentration of the polymer in the composition is between 10 ppm and 500 ppm.
 11. The composition according to claim 1 wherein the composition has a viscosity index greater than
 150. 12. The composition according to claim 1 wherein the composition has a viscosity index greater than
 175. 13. The composition according to claim 1 wherein the composition has a viscosity index greater than
 200. 14. The composition according to claim 1 wherein the composition further includes at least one additional component selected from the group consisting of additional viscosity modifiers, anti-wear additives, dispersants, detergents, pour point depressants, corrosion inhibitors, anti-oxidants, combustion enhancers, and anti-foam agents.
 15. The use of a composition according to claim 1 as a lubricant for an engine.
 16. The use of a composition according to claim 1 as a transmission oil.
 17. The use of a composition according to claim 1 as a hydraulic oil.
 18. A method for reducing deposits in an engine comprising using a composition according to claim 1 as a lubricant. 